Great toe implant devices have been used to replace the defective natural metatarsophalangeal (MTP) joints. Hemi-joint replacement is generally preferred to full joint replacement when the proximal phalanx in the great toe still has good bone stock and the first metatarsal has an integral head. The implants are used to remove pain in the first metatarsal joint incurred from inflammatory arthritis and to restore joint kinetics by replacing the damaged base portion of the proximal phalanx.
U.S. Pat. No. 5,326,366 to Pascerella et. al. discloses an implant device which has an elliptical base with a concave bearing surface that has an anafomically shaped proximal articular surface with an enlarged build-up on the lateral end thereof, and an elongated stem extends distally from the seating surface of the base which includes an array of fins together having a cruciate-shaped cross-section.
U.S. Pat. No. 5,725,585 to Zobel shows a phalangeal component that has an anatomically correct concave bearing surface, a stem that is a trapezoid in cross-section, and spikes on the rear surface of the implant engaging in the proximal phalanx, preventing rotation of the implant.
A proximal phalanx implant in any of the above prior art has a stem projecting perpendicular from the centre of the base. This is anatomically incorrect when the implant is inserted into the bone. The proximal base of the proximal phalanx has an angular relation to the shaft of the proximal phalanx. As the result, the maximum stability of the implant can not be achieved.
The present invention describes an improved implant with a generally ovoid bone plate having a concave bearing surface reciprocal to the shape of a head of a metatarsal bone. The implant includes a stem that has a generally anatomical relationship to the intramedulary canal of a proximal phalanx. In a preferred embodiment, the stem of the implant of the present invention is surface treated and/or, grooved, making it possible to surgically implant the device without bone cement, and with less surface preparation.
It will be understood that there is a need for the development of an improved great toe implant that provides maximum stability and optimal fixation to the bone for a long period of time, which is relatively straightforward for a surgeon to implant, with or without bone cement.